Got it.
Had a look see,
Set DNS back to default ISP DNS, DNS Relay is ON. SPI is OFF, NAT is End Point. Re-enabled Traffic Shaping and set for 1024Mb Uplink for his 512k ISP SPEED. QOS is disabled for now. Port Forwarding is being used.
Mentioned that a downloader he uses could play a part in this as it might seem to cause the DNS to fail more often.
I checked System Check and pings were successful for google and facebook and one LAN device.
Ask him to test settings for now, then also try using manual DNS IPs and turn OFF DSN Relay and test.
Test with and with out the downloader running.
Do a speedtest.net to verify your ISP Speeds. I should have done this with you. Sorry.
Windows 8 firewall is enabled and told hiim that this could be disabled at some point as it's not needed.
Keep us posted.